Modern cellular wireless systems consist of numerous subnets that are interconnected into one or more core networks. Each subnet may correspond, approximately, to a city or another geographic region, and may contain several thousands of cells—each of which may be equipped with one or more Base Stations (BS) (also interchangeably referred to herein as Base Transceiver Stations (BTS)). FIG. 1 is a simplified illustration of an exemplary cellular wireless system 10 with two subnets 12, 14. It is understood that, in practice, there may be many more such subnets and system-specific communication elements (e.g., gateways, routers, switching units, etc.) in the wireless system 10 than those shown in FIG. 1. Each subnet 12, 14 may contain multiple cells and cell-specific one or more BS's/BTS's. In FIG. 1, for the sake of clarity, only some of such cells (e.g., cells 16-19 in subnet 12 and cells 20-24 in subnet 14) and BS's (e.g., BS's 26-29 in subnet 12 and BS's 30-34 in subnet 14) are identified by reference numerals. For the sake of illustration, the geographical “boundary” between subnets 12, 14 is identified by reference numeral “35” in FIG. 1. The base stations or BTS's in a subnet may be collectively controlled by a gateway or control node (such as, for example, the gateway/control node 36 controlling all BTS's in the subnet 12 and the gateway/control node 38 controlling all BTS's in the subnet 14 as shown in FIG. 1). Such gateway/control node of a subnet may function as an aggregator of traffic (originating from or going to the corresponding subnet) and support mobility within the wireless network or system 10. In FIG. 1, each subnet-specific gateway/control node 36, 38 is shown to be connected to a core network 40 of the wireless system 10, thereby providing interconnection between subnets 12, 14 so as to facilitate mobility, customer account management, and seamless access to external networks (e.g., the Internet) (not shown) for User Equipments (UEs) (not shown) operating within each subnet.
The primary function of a BS/BTS (e.g., any of the base stations shown in FIG. 1) is to transmit RF signals in the form of electromagnetic energy over a frequency spectrum (e.g., 20 MHz) to a UE under the RF coverage of the BS within the corresponding cell. In a large wireless network, each transmitter (in a BS/BTS) (not shown) consumes some amount of electrical energy, and, in the aggregate, all such transmitters (of base stations in multiple subnets in a wireless network) may consume significant electrical power. Hence, electrical power consumption becomes a significant part of a wireless operator's Operational Expense (OpEx). Magnified across a nationwide network, conservation of power consumption—even at moderate levels at each cell site—can have a significant and measurable impact on the operator's OpEx.
Overall, power consumption has not been traditionally an emphasis of the advances in wireless technology. Efforts to invest in power saving methods and techniques within the standards-setting bodies had been quite recent. For example, the more recently established specifications-developing body Third Generation Partnership Project 2 (3GPP2) has finally attempted to address such power consumption issues in more detail. In any event, it is observed that, in normal operations, electrical power consumption in a wireless system is positively proportional to the amount of data that the wireless system transmits (using its base stations).
FIG. 2 is an exemplary block diagram of logical processing units of a Base Station (BS) 42 in a Multi-Carrier Power Amplifier (MCPA) system such as, for example, a narrow-band Code Division Multiple Access (CDMA) system. For ease of illustration, only two such carriers (referred to as “carrier 1” and “carrier 2” in FIG. 2) and associated Transmit/Receive (Tx/Rx) chains 44-45 are shown in the multi-carrier configuration of FIG. 2. However, it is understood that many more such carriers and corresponding carrier-specific Tx/Rx chains may be present in the base station 42. Furthermore, the ovals representing Tx/Rx chains 44-45 are for illustration only, and they do not form part of any signal flow or circuit component in the BS 42. Referring again to FIG. 2, after carrier-specific initial signal processing (e.g., coding, modulation, etc.) at blocks 47-48, each carrier-specific Downlink (DL) signal (i.e., transmissions from the BS 42 to one or more UEs (not shown) in the MCPA system) may be transmitted via one or more BS antennas 50 using a corresponding Tx chain (i.e., Tx portions of the Tx/Rx chains 44-45) that may include a respective Analog-to-Digital Converter (ADC) 50-51, a respective Power Amplifier (PA) 53-54, and a respective duplexer unit 56-57. Signals received by the antenna 50 (i.e., Uplink (UL) signals from one or more UEs in the MCPA system) may be initially processed by each carrier-specific Rx chain (i.e., Rx portions of the Tx/Rx chains 44-45) that may include the respective duplexer 56-57, a respective Low Noise Amplifier (LNA) 59-60, and a respective Digital-to-Analog Converter (DAC) 62-63. The received UL analog signals at the outputs of DAC units 62-63 may be then processed (e.g., demodulated, decoded, etc.) using corresponding carrier-specific signal processing blocks 47-48 as shown in FIG. 2.
U.S. Pat. No. 6,584,330 (hereafter, “the '330 patent”) to Tauno Ruuska and assigned to the same assignee as that of the present application describes a method and mechanism for reducing power consumption in an MCPA system. In the '330 patent, a larger spectrum of the wireless system is sub-divided into carrier frequencies F1, F2, . . . , Fn. Each carrier has its own transmission (Tx) and receive (Rx) chain (as shown, for example, in FIG. 2 in the context of a two carrier-based MCPA system), and forms a subsystem independently. Usually, when the loading of the system—as defined by the demand on the system (i.e., for example, an MCPA-based base station such as the BS 42 in FIG. 2) to transmit user data in DL (or to enable transmission of user data in UL)—is the highest, every carrier (from carriers F1, F2, . . . , Fn) is fully occupied, and therefore transmitting. However, as per the '330 patent, when the system loading is lower, one or more of the carriers can be shut down. FIG. 3 illustrates such shutting down of one or more carriers in an MCPA system during off-peak hours. As shown in FIG. 3, during peak hour traffic, all carriers (over the entire system-wide frequency spectrum 65) may be used for transmissions by the MCPA-based BS (e.g., the BS 42), but, during idle or off-peak hours, one or more carriers can be shut down. Such shut-down carriers and associated frequency spectra are shown by hatched portions and collectively identified by reference numeral 67 in FIG. 3. Carrier 1 in FIG. 3 (or carrier 1 in the context of FIG. 2) may be the “primary” carrier and can always remain turned on—i.e., its Power Amplifier (PA) and transmission/reception circuitry (in the corresponding Tx/Rx chain, such as the Tx/Rx chain 44 in FIG. 2) can continue to transmit (and receive). However, carrier 2 and other carriers in FIG. 3 (or carrier 2 in the context of FIG. 2) are “additional” carriers and can be turned off to preserve power consumption. (In the context of FIG. 2, dotted arrows are shown for uplink and downlink communications on carrier 2 to indicate that this carrier can be turned off, if desired.) When a carrier is “turned off” (i.e., when the system or BS 42 is not transmitting or receiving on that carrier), associated Power Amplifier (PA) for that carrier and carrier-specific transmission/reception circuitry (e.g., in the corresponding Tx/Rx chain) can be powered off in order to save energy consumption.